Semiconductor light emitting device and method for producing the same

ABSTRACT

A light emitting device includes: a plurality of n-type III-V group compound semiconductor layers; a plurality of p-type III-V group compound semiconductor layers; and an active layer. Carbon atoms and II-group element atoms are both added to at least one of the plurality of p-type III-V group compound semiconductor layers. Alternatively, carbon atoms and Si atoms are both added to at least one of the plurality of n-type III-V group compound semiconductor layers. Another semiconductor light emitting device has a current blocking structure formed on the double hetero (DH) junction structure, and the current blocking structure at least includes a two-layered n-type current blocking layers including a Se-doped n-type first current blocking layer provided closer to the DH junction structure and a Si-doped n-type second current blocking layer formed on the n-type first current blocking layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of patent Ser. No. 09/073,106 now U.S.Pat. No. 6,183,723 filed May 5, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a III-V group compound semiconductorlight emitting device such as a semiconductor laser device or a lightemitting diode (LED) device, and a method for producing the same.

2. Description of the Related Art

A III-V group compound semiconductor light emitting device such as asemiconductor laser device or an LED device generally has at least one(typically a plurality of) crystal growth layer of the p-typeconductivity (hereinafter, referred to also as the “p-type layer”) andat least one (typically a plurality of) crystal growth layer of then-type conductivity (hereinafter, referred to also as the “n-typelayer”). These crystal growth layers are typically formed by using acrystal growth method such as a liquid phase epitaxial (LPE) method, amolecular beam epitaxial (MBE) method, or a metalorganic chemical vapordeposition (MOCVD) method, which is excellent in mass productivity andallows a very thin film to be grown.

In the LPE method, although a high quality semiconductor crystal can beformed with a relatively simple apparatus, it is difficult to produce auniform crystal over a large area. On the other hand, the MBE method andthe MOCVD method are more suitable processes for mass production, andare widely used at present. The MBE method is a process in which solidelements forming a compound semiconductor are heated in a high vacuumand a substrate is irradiated with beams of the evaporated elements.With this method, a pure crystal can be relatively easily obtained. Inthe MOCVD method, under an atmospheric pressure or a pressuredepressurized to about {fraction (1/10)} atm, elements forming acompound semiconductor are carried in a gaseous form such as an organiccompound or a hydrogen compound, so as to be chemically reacted on asubstrate, thereby forming an intended compound semiconductor.

FIG. 1 is a cross-sectional view illustrating a typical structure of aIII-V group compound semiconductor laser device produced by using theMOCVD method.

In the cross-sectional view of FIG. 1, an n-type GaAs buffer layer 1, ann-type AlGaAs cladding layer 2, an AlGaAs active layer 3, a p-typeAlGaAs first cladding layer 4, a p-type GaAs etching stop layer 5, ap-type AlGaAs second cladding layer 6 and a p-type GaAs protective layer7 are deposited in this order on an n-type GaAs substrate 14, therebyforming a layered structure. In this layered structure, the layers abovethe p-type GaAs etching stop layer 5 form a stripe-shaped mesa structure(a mesa stripe). An n-type AlGaAs current blocking layer 8, an n-typeGaAs current blocking layer 9 and a p-type GaAs planarizing layer 10 areburied on both sides of the mesa stripe.

Moreover, a p-type GaAs contact layer 11 is formed on the p-type GaAsprotective layer 7 and p-type GaAs planarizing layer 10. A p-side metalelectrode 12 and an n-side metal electrode 13 are respectively formed onthe p-type GaAs contact layer 11 and on the reverse surface of then-type GaAs substrate 14 by, for example, a vapor deposition method.

FIG. 2 is, a cross-sectional view illustrating another typical structureof a III-V group compound semiconductor laser device produced by usingthe MOCVD method.

In the cross-sectional view of FIG. 2, a Se-doped n-type GaAs bufferlayer 22, a Se-doped n-type AlGaAs cladding layer 23, an undoped AlGaAsactive layer 24, a Zn-doped p-type first cladding layer 25 and aSe-doped n-type AlGaAs current blocking layer 26 are formed in thisorder on an n-type GaAs substrate 21. A portion of the n-type currentblocking layer 26 is removed in a stripe-shaped pattern, thereby forminga current path 17. A Zn-doped p-type second cladding layer 28 and aZn-doped p-type contact layer 29 are formed on the n-type currentblocking layer 26 including the stripe-shaped portion 17. A p-sideelectrode 18 and an n-side electrode 19 are respectively formed on thep-type contact layer 29 and on the reverse surface of the n-type GaAssubstrate 21.

FIG. 3 is a diagram schematically illustrating a structure of a vapordeposition apparatus of a depressurized horizontal RF heating furnacetype which can be used for growing the semiconductor layers included inthe semiconductor laser device illustrated in FIG. 1 or 2.

In the apparatus illustrated in FIG. 3, trimethylgallium (TMGa),trimethylaluminum (TMAl) or trimethylindium (TMIn) is used as aIII-group material compound; arsine (AsH₃) or phosphine (PH₃) as aV-group material compound; monosilane (SiH₄), disilane (Si₂H₆) orhydrogen selenide (H₂Se) as an n-type dopant material; and diethylzinc(DEZn), dimethylzinc (DMZn) or trimethylarsenic (TMAs) as a p-typedopant material. Carbon tetrachloride (CCl₄) may also be used as acarbon source.

In a crystal growth process, a substrate is placed inside a reactionchamber (growth chamber) 30, the internal pressure of the reactionchamber 30 is set to a predetermined value (e.g., about 76 Torr), andthe substrate temperature is set to a predetermined value (e.g., about700° C.) using an RF coil 31. Then, mass flow controllers (MFCs) andvalves are appropriately controlled to appropriately select, and set theflow rate of, the respective materials from material sources 32 to 38and hydrogen supplied from a hydrogen source through a line 39 so as tosupply them into the reaction chamber 30 through respective supply lines40 to 43, thereby growing an intended semiconductor layer on thesubstrate. Any unwanted gas which may exist in the reaction chamber 30is exhausted through a line 44.

For example, when forming an n-type AlGaAs layer, ASH₃, TMGa, TMAl andan appropriate n-type dopant material are supplied onto the substrate.When forming a Zn (zinc) doped p-type AlGaAs layer, AsH₃, TMGa, TMAl andDMZn or DEZn are supplied onto the substrate. When forming a C (carbon)doped p-type AlGaAs layer, TMAs, AsH₃, TMGa and TMAl are supplied ontothe substrate.

In the MOCVD method, it is likely that organic matter or hydrogengenerated after a chemical reaction may be introduced as an impurityinto a growing compound semiconductor layer. Particularly, carbon (C)contained in organic matter, when introduced into the compoundsemiconductor layer, may act as a p-type dopant. Thus, it is likely thata certain amount of carbon may be present in the grown compoundsemiconductor layer even when carbon tetrachloride (CCl₄) is notsupplied.

For example, when forming a p-type AlGaAs layer with a highconcentration of zinc added thereto, the crystal growth process isperformed while reducing the substrate temperature from about 700° C. toabout 600° C. during the growth process. Then, a certain amount ofcarbon atoms are introduced into an AlGaAs crystal layer obtainedthrough the crystal growth process by the MOCVD method. As the Al molefraction increases carbon atoms are increasingly likely to beintroduced. Therefore, carbon atoms, though at a concentration lowerthan the predetermined zinc atom concentration, will be present in thegrown p-type AlGaAs layer.

When forming a p-type AlGaAs layer with a high concentration of carbonadded thereto, the crystal growth process is performed while reducingthe supply ratio between the V-group material and the III-group material(V/III ratio) from about 60 to about 2 during the growth process. Alsoin this case, carbon atoms will be present at a concentration of, forexample, about 1×10¹⁷ cm⁻³ in the adjacent n-type AlGaAs layer to whichcarbon is not intended to be added.

Moreover, as can be seen from the above description of the structure ofthe apparatus illustrated in FIG. 3, in the formation of a compoundsemiconductor layer by the MOCVD method, Se or Si is used as the n-typedopant element, and Zn, Mg, C, or the like, is typically used as thep-type dopant element. These dopants should be controlled so as to bepresent at a predetermined concentration in the intended crystal growthlayer. When one of the dopants is used alone, the doping conditions suchas the concentration may be controlled relatively easily. However, thesedopants diffuse as the substrate is heated during the growth process,whereby an intended concentration profile may not be obtained. Moreover,in the case of a layered structure, complex mutual diffusion of thedopants may occur depending upon the combination of the materials of theadjacent layers or the combination of the dopant types used.

For example, Zn, Be, Mg, or the like, which are II-group elements andused as p-type dopants, are impurities which may diffuse relativelyeasily, and are difficult to control. Particularly, when such an elementis added at a high concentration, precipitation at the interface betweenthe p-type crystal growth layer and the n-type crystal growth layer (thep-n interface), or diffusion toward the substrate surface, occurssignificantly.

On the other hand, carbon, which also acts as a p-type dopant, has asmall diffusion coefficient, and thus is often used in HBTs or HEMTs.However, when carbon is used as the p-type dopant in a semiconductorlight emitting device, although the carbon itself does not diffuse,diffusion of Si or Se used as an n-type dopant may cause a problem thatthe C doped p-type layer is inverted to the n-type.

Moreover, when only carbon as a p-type dopant is added into a crystallayer of a III-V group compound semiconductor, in order to realize anintended amount of addition, it is typically required to set the supplyratio between the V-group material and the III-group material (V/IIIratio) at a small value. However, under such a setting, it is likelythat an impurity such as oxygen or water, in addition to carbon, may beintroduced into the crystal layer, whereby the electrical and/or opticalcharacteristics of the obtained p-type III-V group compoundsemiconductor crystal layer may deteriorate.

On the other hand, when only zinc as a p-type dopant is added into acrystal layer of a III-V group compound semiconductor, in order torealize an intended amount of addition, it is typically required to setthe substrate temperature during the crystal growth process at a smallvalue, as described previously. However, under such setting, it islikely that an impurity such as oxygen or water is introduced into thecrystal layer, whereby the electrical and/or optical characteristics ofthe obtained p-type III-V group compound semiconductor crystal layer maydeteriorate.

Furthermore, due to the mutual diffusion of Zn as a p-type dopant and Seas an n-type dopant, the Zn-doped layer, which should be of the p-type,may not always be of the p-type; i.e., conductivity type inversion mayoccur. For example, in the structure illustrated in FIG. 2, the p-typefirst cladding layer 25 may be inverted to the n-type, whereby then-type cladding layer 23 and the n-type current blocking layer 26 may beshort-circuited with each other. Alternatively, a portion of the n-typecladding layer 23 directly beneath the stripe-shaped portion 17, in thevicinity of the active layer 24, may be inverted to the p-type, wherebyan increase in the operating current (a decrease in reliability) mayoccur.

In order to suppress such mutual diffusion, Si may be used instead of Seas an n-type dopant. Si is a dopant which is typically less likely todiffuse and has an effect of suppressing diffusion of a p-type dopant atthe p-n interface into the n-type layer. However, such an effect ofsuppressing the p-type dopant diffusion into the n-type layer maycontrarily lower the operating characteristics of the produced lightemitting device.

In particular, when the n-type dopant in the structure illustrated inFIG. 2 is Se exhibiting no diffusion suppressing effect, due to thediffusion of Zn as a p-type dopant added to the p-type cladding layer25, the carrier concentration of the p-type cladding layer 25 in regionsbeneath the current blocking layer 26 becomes lower than that in anotherregion beneath the stripe-shaped portion 17. On the other hand, when Siis used in stead of Se as an n-type dopant, Si remains in the n-typecladding layer 23 and the n-type current blocking layer 26, and Zn as ap-type dopant added to the p-type cladding layer 25, except for a smallamount thereof diffusing into the active layer 24, remains in the p-typecladding layer 25 due to the diffusion suppressing effect of Si. As aresult, the carrier concentration of the p-type cladding layer 25 issubstantially the same in the region beneath the stripe-shaped portion17 and in the region beneath the current blocking layer 26. Therefore,the resistance of the p-type cladding layer 25 decreases while theleakage current increase, whereby there occurs a problem of a largeoperating current.

As described above, in accordance with the conventional techniques, itis not possible to reliably suppress diffusion of dopants contained inthe respective compound semiconductor layers of the III-V group compoundsemiconductor light emitting device. Therefore, it is difficult toreliably control the dopant concentration or the conductivity type ofthe respective layers, whereby the operating characteristics of theresultant light emitting device may deteriorate.

SUMMARY OF THE INVENTION

A light emitting device of the present invention includes: a pluralityof n-type III-V group compound semiconductor layers; a plurality ofp-type III-V group compound semiconductor layers; and an active layer,wherein carbon atoms and II-group element atoms are both added to atleast one of the plurality of p-type III-V group compound semiconductorlayers.

Preferably, a ratio ([C]/[II-group element]) between a concentration ofthe carbon atoms [C] and a concentration of the II-group element atoms[II-group element], which are both added to the p-type III-V groupcompound semiconductor layer, is in a range between about 1 and about10.

The p-type III-V group compound semiconductor layer, to which the carbonatoms and the II-group element atoms are both added, may be in contactwith at least one of the plurality of n-type III-V group compoundsemiconductor layers.

The p-type III-V group compound semiconductor layer, to which the carbonatoms and the II-group element atoms are both added, may be in contactwith the active layer.

Another aspect of the present invention provides a method for producinga semiconductor light emitting device. The method includes the step ofgrowing a layered structure on a surface of a substrate. The layeredstructure at least includes a plurality of n-type III-V group compoundsemiconductor layers, a plurality of p-type III-V group compoundsemiconductor layers, and an active layer. Carbon atoms and II-groupelement atoms are both added when growing at least one layer of theplurality of p-type III-V group compound semiconductor layers.

Another semiconductor light emitting device of the present inventionincludes: a plurality of n-type III-V group compound semiconductorlayers; a plurality of p-type III-V group compound semiconductor layers;and an active layer, wherein carbon atoms and Si atoms are both added toat least one of the plurality of n-type III-V group compoundsemiconductor layers.

The n-type III-V group compound semiconductor layer, to which the carbonatoms and the Si atoms are both added, may be in contact with at leastone of the plurality of p-type III-V group compound semiconductorlayers.

Still another aspect of the present invention provides another methodfor producing a semiconductor light emitting device. The method includesthe step of growing a layered structure on a surface of a substrate. Thelayered structure at least includes a plurality of n-type III-V groupcompound semiconductor layers, a plurality of p-type III-V groupcompound semiconductor layers, and an active layer. Carbon atoms and Siatoms are both added when growing at least one layer of the plurality ofn-type III-V group compound semiconductor layers.

Still another semiconductor light emitting device of the presentinvention includes: an n-type substrate; a double hetero junctionstructure formed on the n-type substrate, the double hetero junctionstructure at least including a Si-doped n-type cladding layer, an activelayer, and a Zn-doped p-type first cladding layer; and a currentblocking structure formed on the double hetero junction structure. Thecurrent blocking structure at least includes an n-type current blockinglayer and a second p-type cladding layer. The n-type current blockinglayer includes: a Se-doped n-type first current blocking layer adjacentto the Zn-doped p-type first cladding layer; and a Si-doped n-typesecond current blocking layer formed on the n-type first currentblocking layer.

In one embodiment, in the current blocking structure, the n-type currentblocking layer has a stripe-shaped groove, and the p-type secondcladding layer is formed so as to cover the groove and the n-typecurrent blocking layer.

In another embodiment, in the current blocking structure, the p-typesecond cladding layer has a striped ridge shape, and the n-type currentblocking layer is provided on both sides of the ridge shape.

Preferably, an amount of Zn, which is represented as a product of apreset Zn concentration in the p-type first cladding layer and athickness of the p-type first cladding layer, is equal to or greaterthan an amount of Se, which is represented as a product of a preset Seconcentration in the n-type first current blocking layer and a thicknessof the n-type first current blocking layer.

The p-type second cladding layer and the n-type current blocking layermay be layers which are regrown by an MOCVD method or an LPE method.

Thus, the invention described herein makes possible the advantages of:(1) providing a semiconductor light emitting device with satisfactoryoperating characteristics by reliably suppressing diffusion of dopantscontained in the respective compound semiconductor layers of thesemiconductor light emitting device to reliably control the dopantconcentration or the conductivity type of the respective layers; and (2)providing a method for producing such a semiconductor light emittingdevice.

These and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a typical structure of aIII-V group compound semiconductor laser device produced by using theMOCVD method.

FIG. 2 is a cross-sectional view illustrating another typical structureof a III-V group compound semiconductor laser device produced by usingthe MOCVD method.

FIG. 3 is a diagram schematically illustrating a structure of a vapordeposition apparatus of a depressurized horizontal RF heating furnacetype which can be used for growing the semiconductor layers included inthe semiconductor laser device illustrated in FIG. 1 or 2.

FIG. 4 is a cross-sectional view illustrating a structure of asemiconductor light emitting device according to Example 1 of thepresent invention.

FIG. 5 illustrates secondary ion mass spectrometry (SIMS) profiles forconcentrations of n-type and p-type dopants in the current blockingstructure of the semiconductor light emitting device illustrated in FIG.4.

FIG. 6 illustrates secondary ion mass spectrometry (SIMS) profiles forconcentrations of n-type and p-type dopants in a device which isproduced so that only Zn is added to the respective layers formed ofp-type GaAs and AlGaAs in the same structure as that of thesemiconductor light emitting device illustrated in FIG. 4.

FIG. 7 illustrates secondary ion mass spectrometry (SIMS) profiles forconcentrations of n-type and p-type dopants in a device which isproduced so that only carbon is added to the respective layers formed ofp-type GaAs and AlGaAs in the same structure as that of thesemiconductor light emitting device illustrated in FIG. 4.

FIG. 8 illustrates secondary ion mass spectrometry (SIMS) profiles forconcentrations of n-type and p-type dopants in a device which isproduced so that the ratio ([C]/[Zn]) between the carbon atomconcentration [C] and the zinc atom concentration [Zn] is less than 1 inthe respective layers formed of p-type GaAs and AlGaAs in the samestructure as that of the semiconductor light emitting device illustratedin FIG. 4.

FIG. 9 illustrates secondary ion mass spectrometry (SIMS) profiles forconcentrations of n-type and p-type dopants in a device which isproduced so that the ratio ([C]/[Zn]) between the carbon atomconcentration [C] and the zinc atom concentration [Zn] is 1 or greaterin the respective layers formed of p-type GaAs and AlGaAs in the samestructure as that of the semiconductor light emitting device illustratedin FIG. 4.

FIG. 10 is a cross-sectional view illustrating a structure of asemiconductor light emitting device according to Example 2 of thepresent invention.

FIG. 11 illustrates secondary ion mass spectrometry (SIMS) profiles forconcentrations of n-type and p-type dopants in the current blockingstructure of the semiconductor light emitting device illustrated in FIG.10.

FIG. 12 illustrates secondary ion mass spectrometry (SIMS) profiles forconcentrations of n-type and p-type dopants in a device which isproduced so that only carbon is added to the respective layers formed ofp-type GaAs and AlGaAs in the same structure as that of thesemiconductor light emitting device illustrated in FIG. 10.

FIG. 13 illustrates secondary ion mass spectrometry (SIMS) profiles forconcentrations of n-type and p-type dopants in a device which isproduced so that only Be is added to the respective layers formed ofp-type GaAs and AlGaAs in the same structure as that of thesemiconductor light emitting device illustrated in FIG. 10.

FIG. 14 is a cross-sectional view illustrating a structure of asemiconductor light emitting device according to Example 3 of thepresent invention.

FIG. 15 is a cross-sectional view illustrating a structure of asemiconductor light emitting device according to Example 4 of thepresent invention.

FIGS. 16A to 16D are cross-sectional views each illustrating aproduction process of a semiconductor light emitting device illustratedin FIG. 15.

FIG. 17 is a cross-sectional view illustrating a structure of asemiconductor light emitting device according to Example 6 of thepresent invention.

FIG. 18 is a cross-sectional view illustrating a structure of asemiconductor light emitting device according to Example 8 of thepresent invention.

FIG. 19 illustrates SIMS profiles for a sample produced according toExample 8 of the present invention.

FIG. 20 illustrates other SIMS profiles for the sample producedaccording to Example 8 of the present invention.

FIG. 21 is an enlarged view illustrating a portion of the SIMS profilesillustrated in FIG. 20.

FIG. 22 is a cross-sectional view illustrating a structure of asemiconductor light emitting device according to Example 10 of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE 1

Hereinafter, a semiconductor light emitting device (semiconductor laserdevice) which is produced using both Zn and carbon as p-type dopantswill be described as Example 1 of the present invention.

FIG. 4 is a cross-sectional view illustrating a structure of asemiconductor laser device according to Example 1 of the presentinvention.

In the cross-sectional view of FIG. 4, an n-type GaAs buffer layer 115,an n-type AlGaAs cladding layer 116, an AlGaAs active layer 117, ap-type AlGaAs first cladding layer 118, a p-type GaAs etching stop layer119, a p-type AlGaAs second cladding layer 120 and a p-type GaAsprotective layer 121 are deposited in this order on an n-type GaAssubstrate 128, thereby forming a layered structure.

In this layered structure, the layers above the p-type GaAs etching stoplayer 119 form a stripe-shaped mesa structure (a mesa stripe). An n-typeAlGaAs current blocking layer 122, an n-type GaAs current blocking layer123 and a p-type GaAs planarizing layer 124 are buried on both sides ofthe mesa stripe. Thus, a current blocking structure for constricting acurrent into the mesa stripe portion is formed.

Moreover, a p-type GaAs contact layer 125 is formed on the p-type GaAsprotective layer 121 and the p-type GaAs planarizing layer 124. A p-sidemetal electrode 126 and an n-side metal electrode 127 are respectivelyformed on the p-type GaAs contact layer 125 and on the reverse surfaceof the n-type GaAs substrate 128 by, for example, a vapor depositionmethod.

The layers included in the semiconductor laser device illustrated inFIG. 4 may be grown by using the vapor deposition apparatus of adepressurized horizontal RF heating furnace type described above withreference to FIG. 3.

In particular, in the apparatus illustrated in FIG. 3, trimethylgallium(TMGa) is used as a Ga material; trimethylaluminum (TMAl) as an Almaterial; arsine (AsH₃) as an As material; monosilane (SiH₄) as a Simaterial as an n-type dopant; diethylzinc (DEZn) as a Zn material, whichis one of the p-type dopants; and trimethylarsenic (TMAs) as a carbonmaterial, which is the other one of the p-type dopants. A substrate isplaced inside the reaction chamber 30, the internal pressure of thereaction chamber 30 is set to about 76 Torr, and the substratetemperature is set to about 700° C. using the RF coil 31. Then, the massflow controllers (MFCs) and the valves are appropriately controlled soas to set the ratio (V/III ratio) between the amount of supply of thematerial compound containing the III-group material (i.e., the amount ofsupply of TMGa, or the total amount of supply of TMGa and that of TMAl)and the amount of supply of the material compound containing the V-groupelement (i.e., the total amount of supply of AsH₃ and that of TMAs) toabout 60. Then, the crystal growth process of the respective layersproceeds while the above-described conditions are kept constant duringthe process.

For example, when growing the n-type GaAs buffer layer 115 and then-type GaAs current blocking layer 123, TMGa, AsH₃ and SiH₄ are suppliedonto the substrate. When forming n-type AlGaAs cladding layer 116 andthe n-type AlGaAs current blocking layer 122, TMGa, TMAl, AsH₃ and SiH₄are supplied onto the substrate. When forming the AlGaAs active layer117, TMGa, TMAl and AsH₃ are supplied onto the substrate. When formingthe p-type GaAs contact layer 125, TMGa, AsH₃ and DEZn are supplied ontothe substrate. Moreover, when growing the p-type GaAs etching stop layer119, the p-type GaAs protective layer 121 and the p-type GaAsplanarizing layer 124, TMGa, AsH₃, DEZn and TMAs are supplied onto thesubstrate. When growing the p-type AlGaAs first cladding layer 118 andthe p-type AlGaAs second cladding layer 120, TMGa, TMAl, AsH₃, DEZn andTMAs are supplied onto the substrate.

In this way, Zn, as a II-group element atom, and carbon are both addedas p-type dopants to the layers 118 to 121 and 124 formed of p-type GaAsor p-type AlGaAs, which are adjacent to the n-type AlGaAs currentblocking layer 122 and the n-type GaAs current blocking layer 123.

The amount of carbon added to the respective layers is controlled bysetting the V/III ratio. Moreover, TMAs is used as the carbon materialcompound in the above description. However, in practice, even when theTMAs supply is omitted, the carbon addition may also be realized due todecomposition of the other material compounds.

FIG. 5 illustrates the secondary ion mass spectrometry (SIMS) profilesfor concentrations of the n-type and p-type dopants in the currentblocking structure of the semiconductor laser device produced asdescribed above in accordance with the present example. FIG. 6illustrates, as a comparative example, the SIMS profiles for a devicewhich is obtained by performing a crystal growth process while reducingthe substrate temperature to about 600° C. so that only Zn is added tothe respective layers formed of p-type GaAs or p-type AlGaAs in the samestructure as that of the present example. Moreover, FIG. 7 illustratesthe SIMS profiles for a device which is obtained by performing a crystalgrowth process while reducing the V/III ratio to about 2 so that onlycarbon is added to the respective layers formed of p-type GaAs or p-typeAlGaAs in the same structure as that of the present example. In FIGS. 5to 7, the horizontal axis represents the depth from the surface of thegrown layered structure, while the vertical axis represents theconcentrations of carbon (C) and zinc (Zn) as p-type dopants and silicon(Si) as an n-type dopant.

Comparison between FIGS. 5 and 6 shows the following. In FIG. 6 whereonly Zn is added, Zn diffuses into the n-type cladding layer 116 and then-type current blocking layers 122 and 123, whereby the dopantconcentration (carrier concentration) in the p-type AlGaAs firstcladding layer 118 is lower than the predetermined value (about 8×10¹⁷cm⁻³). In contrast, in FIG. 5 where Zn and carbon are both used, suchdiffusion of Zn is not caused, whereby the dopant concentration (carrierconcentration) is accurately controlled.

Comparison between FIGS. 5 and 7 shows the following. In FIG. 7 whereonly carbon is added, Si diffuses into the p-type AlGaAs first claddinglayer 118, whereby a portion of the p-type AlGaAs first cladding layer118 in the vicinity of the p-n interface is inverted to n-type. Incontrast, in FIG. 5 where Zn and carbon are both used, such diffusion ofSi or the p-type to n-type inversion associated therewith is not caused.

The carrier concentration of the semiconductor laser device of thepresent example, which exhibits the concentration profile as illustratedin FIG. 5, was determined by a C-V measurement. The result confirmedthat the predetermined value (about 8×10¹⁷ cm⁻³) was obtained.

According to a further study done by the present inventors, when thegrowth temperature (i.e., the substrate temperature during the crystalgrowth process) is set to about 670° C. or higher while setting theV/III ratio to about 20 or higher, contamination of oxygen into thep-type AlGaAs layer is not detected by the SIMS measurement. In otherwords, the amount of oxygen contamination into the p-type AlGaAs layerin the semiconductor laser device of the present example is planarizingreduced compared to that of the conventional techniques.

Hereinafter, the result of a study on the optimal amount of carbon andZn added as p-type dopants in the above-described process will bedescribed.

In particular, in the apparatus illustrated in FIG. 3, a substrate isplaced inside the reaction chamber (growth chamber) 30, the internalpressure of the reaction chamber 30 is set to about 76 Torr, and thesubstrate temperature is set to about 700° C. using the RF coil 31, asdescribed above. Then, the crystal growth process of the layers isperformed under the following two conditions, while the amount of supplyof the material compound containing the III-group material (i.e., theamount of supply of TMGa, or the total amount of supply of TMGa and thatof TMAl) is kept constant by appropriately controlling the mass flowcontrollers (MFCs) and the valves. In the first condition, the V/IIIratio is set so that the ratio ([C]/[Zn]) between the carbon atomconcentration [C] and the zinc atom concentration [Zn] is less than 1 inthe layers 118 to 121 and 124 formed of p-type GaAs or p-type AlGaAs,which are adjacent to the n-type AlGaAs current blocking layer 122 andthe n-type GaAs current blocking layer 123. In the second condition, theV/III ratio is set so that the above ratio ([C]/[Zn]) is 1 or greater.Under such conditions, the layers are grown while adding both Zn, as aII-group element atom, and carbon.

FIGS. 8 and 9 illustrate the secondary ion mass spectrometry (SIMS)profiles for concentrations of the n-type and p-type dopants in thecurrent blocking structure of the semiconductor laser device producedunder the first and second conditions, respectively. In FIGS. 8 and 9,the horizontal axis represents the depth from the surface of the grownlayered structure, while the vertical axis represents the concentrationsof carbon (C) and zinc (Zn) as p-type dopants and silicon (Si) as ann-type dopant.

Comparison between FIGS. 8 and 9 shows the following. In FIG. 8illustrating the results under the first condition (i.e., [C]/[Zn]<1),Zn diffuses into the n-type current blocking layers 122 and 123, wherebythe dopant concentration (carrier concentration) in the p-type AlGaAsfirst cladding layer 118 is lower than the predetermined value (about8×10¹⁷ cm⁻³). In contrast, in FIG. 9 illustrating the results under thesecond condition (i.e., [C]/[Zn]≧1), such diffusion of Zn is not caused,whereby the dopant concentration (carrier concentration) is accuratelycontrolled.

As the further experiments under the second condition, crystal growthprocesses are performed at different [C]/[Zn] ratios by setting thedopant concentration (carrier concentration) in the p-type AlGaAs firstcladding layer 118 to a constant value (about 8×10¹⁷ cm⁻³) while varyingthe zinc atom concentration [Zn] to about 3.5×10¹⁷ cm⁻³, about1.5×10^(17 cm) ⁻³, about 7×10¹⁶ cm⁻³ and about 5×10¹⁶ cm⁻³. As a result,it is confirmed from the SIMS measurement that the diffusion of Si fromthe n-type current blocking layers 122 and 123 into the p-type AlGaAsfirst cladding layer 118 occurs only at the zinc atom concentration [Zn]of about 5×10¹⁶ cm⁻³.

As can be seen from the above description, it is preferable to set the[C]/[Zn] ratio within a range between about 1 to about 10 in order tosuppress the undesirable diffusion of Zn and Si.

As described above, the semiconductor laser device of the presentexample in which Zn, as a II-group compound element atom, and carbon areboth added as p-type dopants can be produced with high reproducibility,thereby planarizing increasing the production yield from that of theconventional techniques. Moreover, the semiconductor laser device of thepresent example stably operated over 5000 hours in a reliability testwith an output of about 35 mW at about 60° C. Thus, a high quality andhigh reliability semiconductor laser device is obtained.

Effects comparable to the above also may be obtained when Se is usedinstead of Si as the n-type dopant. Moreover, effects comparable to theabove may also be obtained when Mg or Be is used instead of Zn as thep-type dopant. Furthermore, the substrate temperature or the V/III ratiomay be set to a value other than the above as long as it is keptconstant during a crystal growth process.

EXAMPLE 2

Hereinafter, a semiconductor light emitting device (semiconductor laserdevice) which is produced using both Be and carbon as p-type dopantswill be described as Example 2 of the present invention.

FIG. 10 is a cross-sectional view illustrating a structure of asemiconductor laser device according to Example 2 of the presentinvention.

In the cross-sectional view of FIG. 10, an n-type GaAs buffer layer 229,an n-type GaInP buffer layer 230, an n-type AlGaInP cladding layer 231,a GaInP active layer 232, a p-type AlGaInP first cladding layer 233, ap-type GaInP etching stop layer 234, a p-type AlGaInP second claddinglayer 235 and a p-type GaAs contact layer 236 are deposited in thisorder on an n-type GaAs substrate 240, thereby forming a layeredstructure.

In this layered structure, the layers above the p-type GaInP etchingstop layer 234 form a stripe-shaped mesa structure (a mesa stripe). Ann-type GaAs current blocking layer 237 is buried on both sides of themesa stripe. Thus, a current blocking structure for constricting acurrent into the mesa stripe portion is formed.

Moreover, a p-side metal electrode 238 and an n-side metal electrode 239are respectively formed on the p-type GaAs contact layer 236 and on thereverse surface of the n-type GaAs substrate 240 by, for example, avapor deposition method.

The layers included in the semiconductor laser device illustrated inFIG. 10 may be grown by performing a crystal growth process using aknown MBE apparatus while setting the substrate temperature to about550° C.

For example, when growing the p-type AlGaInP first cladding layer 233and the p-type AlGaInP second cladding layer 235, the substrate isirradiated with molecular beams of Ga, Al, In, P, Be and C. When growingthe p-type GaInP etching stop layer 234, the substrate is irradiatedwith molecular beams of Ga, In, P, Be and C. Similarly, when growing thep-type GaAs contact layer 236, the substrate is irradiated withmolecular beams of Ga, As, Be and C.

In this way, Be, as a II-group element atom, and carbon are both addedas p-type dopants to the layers 233 to 236 formed of p-type GaAs, p-typeAlGaInP or p-type GaInP, which are adjacent to the n-type GaAs currentblocking layer 237.

The amount of carbon added to the respective layers is controlled bysetting the V/III ratio (i.e., the ratio in the amount of molecular beamirradiation).

FIG. 11 illustrates the secondary ion mass spectrometry (SIMS) profilesfor concentrations of the n-type and p-type dopants in the currentblocking structure of the semiconductor laser device produced asdescribed above in accordance with the present example. FIGS. 12 and 13each illustrate, as a comparative example, the SIMS profiles for adevice which is obtained by a conventional technique where only carbon(as in FIG. 12) or Be (as in FIG. 13) is added to the respective layersformed of p-type GaAs, p-type AlGaInP or p-type GaInP in the samestructure as that of the present example. In FIGS. 11 to 13, thehorizontal axis represents the depth from the surface of the grownlayered structure, while the vertical axis represents the concentrationsof carbon (C) and beryllium (Be) as p-type dopants and silicon (Si) asan n-type dopant.

Comparison between FIGS. 11 and 12 shows the following. In FIG. 12 whereonly carbon is added, Si diffuses into the p-type AlGaInP first claddinglayer 233, whereby a portion of the p-type AlGaInP first cladding layer233 in the vicinity of the p-n interface is inverted to n-type. Incontrast, in FIG. 11 where Be and carbon are both used, such diffusionof Si or the p-type to n-type inversion associated therewith is notcaused.

Comparison between FIGS. 11 and 13 shows the following. In FIG. 13 whereonly Be is added, Be diffuses into the n-type cladding layer 231 and then-type current blocking layer 237, whereby the dopant concentration(carrier concentration) in the p-type AlGaInP first cladding layer 233is lower than the predetermined value (about 1×10¹⁸ cm⁻³). In contrast,in FIG. 11 where Be and carbon are both used, such diffusion of Be isnot caused, whereby the dopant concentration (carrier concentration) isaccurately controlled.

As described above, the semiconductor laser device of the presentexample in which Be, as a II-group compound element atom, and carbon areboth added as p-type dopants can be produced with high reproducibility,thereby planarizing increasing the production yield from that of theconventional techniques. Moreover, the semiconductor laser device of thepresent example stably operated over 5000 hours in a reliability testwith an output of about 5 mW at about 60° C. Thus, a high quality andhigh reliability semiconductor laser device is obtained.

EXAMPLE 3

Hereinafter, a semiconductor light emitting device (LED device) which isproduced using both Zn and carbon as p-type dopants will be described asExample 3 of the present invention.

FIG. 14 is a cross-sectional view illustrating a structure of an LEDdevice according to Example 3 of the present invention.

In the cross-sectional view of FIG. 14, an n-type AlInP cladding layer341, an AlGaInP active layer 342, a p-type AlInP cladding layer 343 anda p-type GaP current diffusion layer 344 are deposited in this order onan n-type GaAs substrate 347, thereby forming a layered structure.Moreover, a p-side metal electrode 345 having a predetermined patternand an n-side metal electrode 346 are respectively formed on the p-typeGaP current diffusion layer 344 and on the reverse surface of the n-typeGaAs substrate 347 by, for example, a vapor deposition method.

The layers included in the LED device illustrated in FIG. 14 may begrown by using the vapor deposition apparatus of a depressurizedhorizontal RF heating furnace type described above with reference toFIG. 3.

In particular, in the apparatus illustrated in FIG. 3, trimethylgallium(TMGa) is used as a Ga material; trimethylaluminum (TMAl) as an Almaterial; trimethylindium(TMIn) as an In material; phosphine (PH₃) as aP material; monosilane (SiH₄) as a Si material as an n-type dopant;diethylzinc (DEZn) as a Zn material, which is one of the p-type dopants;and carbon tetrachloride (CCl₄) as a carbon material, which is the otherone of the p-type dopants. A substrate is placed inside the reactionchamber (growth chamber) 30, the internal pressure of the reactionchamber 30 is set to about 76 Torr, and the substrate temperature is setto about 700° C. using the RF coil 31. Then, the mass flow controllers(MFCs) and the valves are appropriately controlled so as to set theratio (V/III ratio) between the amount of supply of the materialcompound containing the III-group material (i.e., the amount of supplyof TMGa, or the total amount of supply of TMGa, that of TMAl and that ofTMIn) and the amount of supply of the material compound containing theV-group element (i.e., the amount of supply of PH₃) to a predeterminedconstant value. Then, the crystal growth process of the respectivelayers proceeds while the above-described conditions are kept constantduring the process. For example, when growing the p-type AlInP claddinglayer 343, TMAl, TMIn, PH₃, DEZn and CCl₄ are supplied onto thesubstrate.

In this way, Zn, as a II-group element atom, and carbon are both addedas p-type dopants to the p-type AlInP cladding layer 343, which isadjacent to the n-type AlInP cladding layer 341.

For the LED device of the present example produced as described aboveand a device which is obtained by a conventional technique where only Znis added to the p-type AlInP cladding layer 343 in the same structure asthat of the present example, the concentrations of the n-type and p-typedopants were measured by the secondary ion mass spectrometry (SIMS). Theresults confirms that the amount of Zn diffused into the AlGaInP activelayer 342 and the n-type AlInP cladding layer 341 is reduced in thedevice of the present example. Such reduction in the amount of diffusionremarkably improves the luminance of light emitted from the LED.

Thus, in accordance with the present example, an LED device exhibitinghigh quality and high luminance of the emitted light is obtained.

In accordance with the above-described Examples 1 to 3 of the presentinvention, in a III-V group compound semiconductor light emitting devicehaving a plurality of n-type III-V group compound semiconductor layersand a plurality of p-type III-V group compound semiconductor layers, aII-group element atom such as Zn, Be, or the like, and carbon are bothadded as p-type dopants to at least one of the p-type III-V groupcompound semiconductor layers. Moreover, the ratio ([C]/[II-groupelement]) between the carbon atom concentration [C] and the II-groupelement concentration [II-group element] in the p-type III-V groupcompound semiconductor layer is preferably set within a range betweenabout 1 to about 10. Thus, the II-group element atoms as a p-type dopantin the p-type layer combine with the n-type dopants in the n-type layer(e.g., Si or Se) at the p-n interface, thereby suppressing the diffusionof the n-type dopant or the p-type to n-type inversion associatedtherewith.

Such combining between the dopants may cause precipitation of theII-group element atoms at the p-n interface, whereby the II-groupelement concentration in the p-type layer decreases. However, carbon asthe other p-type dopant is less likely to diffuse, it remains in thep-type layer, whereby a predetermined dopant concentration (carrierconcentration) in the p-type layer is maintained. As a result, theoperating characteristics of the produced semiconductor light emittingdevice such as a semiconductor laser device or an LED device areimproved while the production yield thereof is also improved.

Furthermore, unlike the conventional techniques, it is not necessary toreduce the V/III ratio or the substrate temperature during the crystalgrowth process. Therefore, it is less likely that an impurity such asoxygen or water is introduced into the crystal growth layer, whereby aIII-V group compound semiconductor crystal layer having satisfactorycrystallinity would be grown on a crystal substrate. This also improvesthe operating characteristics of the produced semiconductor lightemitting device, such as a semiconductor laser device or an LED device,and the production yield thereof.

EXAMPLE 4

In the above-described examples, carbon and a II-group element are bothused as p-type dopants so as to control the p-type dopant. In thefollowing Example 4, carbon is used for the purpose of controlling then-type dopant.

FIG. 15 is a cross-sectional view illustrating a III-V group compoundsemiconductor laser device produced in accordance with the presentexample.

In the cross-sectional view of FIG. 15, an n-type GaAs buffer layer 402,an n-type Al_(0.5)Ga_(0.5)As cladding layer 403, an undopedAl_(0.15)Ga_(0.85)As active layer 404 and a p-type Al_(0.5)Ga_(0.5)Ascladding layer 405 are formed in this order on an n-type GaAs substrate401. The p-type cladding layer 405 is formed so as to have astripe-shaped convex portion on the upper side thereof, and an n-typeGaAs current blocking layer 406 is buried on both sides of the stripe,thereby forming a current blocking structure where the striped portionfunctions as a current path.

A p-type GaAs intermediate layer 407 is formed on the striped portion,and a p-type GaAs contact layer 409 is further formed on the p-type GaAsintermediate layer 407 and the n-type GaAs current blocking layer 406.The p-side and n-side electrodes are omitted in FIG. 15. Moreover, theformation of the p-type GaAs intermediate layer 407 may be omitted.

The relationship among the composition ratios of the respective layersmay be generalized as follows. An Al_(x)Ga_(1−x)As cladding layer of thefirst conductivity type, an Al_(y)Ga_(1−y)As active layer, anAl_(x)Ga_(1−x)As cladding layer of the second conductivity type and anAl_(z)Ga_(1−z)As current blocking layer of the first conductivity typeare formed so that the mole fractions of x, y and z representing theAlAs-GaAs crystal ratio satisfy the relationship:

x>y≧0 and z≧0; or z>x>y ≧0.

When producing a semiconductor laser device having the above structure,in accordance with the present example, carbon, as well as Si as ann-type dopant, is added in the growth process of an n-type layer.

The present inventors conducted a detailed study on the diffusionphenomenon of the p-type dopant which makes it difficult to control theconductivity type of the p-type layer in a double hetero (DH) junctionstructure formed of p-type and n-type cladding layers and an activelayer. As a result, the present inventors have found that the diffusionof the p-type dopant is associated with the presence of interstitial Gaatoms in the base crystal and that the interstitial Ga atoms can bereduced by using Si as an n-type dopant which occupies the III-groupsite, thereby reducing the diffusion of the p-type dopant.

However, a Si atom is an amphoteric, and it can be introduced into theV-group site, instead of the III-group site, thereby exhibiting thereverse conductivity type. In view of this, the present inventors madean attempt to prevent the Si atoms from being introduced into theV-group site and thus exhibiting the reverse conductivity type, bysupplying carbon, which is introduced only into the V-group site, alongwith Si with high controllability in a growth process of the n-typelayer. As a result, it was confirmed that Si atoms were efficientlysupplied to the III-group site, thereby exhibiting the intendedconductivity type. Thus, it is possible to stably produce asemiconductor laser device (semiconductor light emitting device) withhigh reliability.

For simultaneously supplying carbon for such a purpose, in accordancewith the present example, the substrate temperature during the crystalgrowth process is set to about 700° C. to about 800° C. (typically,about 700° C.), while the V/III ratio is set to about 20 to about 500(typically, about 120). Particularly, by controlling the V/III ratio,the carbon addition concentration is substantially linearly controlled,whereby the carbon addition concentration increases as the V/III ratiois reduced. This is done by, for example, maintaining the suppliedamount of the material compound containing the III-group element at aconstant value while varying the supplied amount of the materialcompound containing the V-group element.

The carbon addition concentration in the formation of the n-type layer,may be of any value which dose not exceed the predetermined n-typedopant concentration (carrier concentration). More particularly, whenthe carbon addition concentration is about 1×10¹⁵ cm⁻³ to about 1×10¹⁸cm⁻³, Si atoms may be efficiently introduced into the III-group siteswithin a atom concentration range between about 1×10¹⁶ cm⁻³ and about2×10¹⁸ cm⁻³.

In the structure illustrated in FIG. 15, an electric current is injectedthrough the p-type GaAs contact layer 409, and flows through the stripedportion of the p-type Al_(0.5)Ga_(0.5)As cladding layer 405 due to thepresence of the n-type GaAs current blocking layer 406, thereby flowingin a concentrated manner into a region of the Al_(0.15)Ga_(0.85)Asactive layer 404 beneath the striped portion and generating laseroscillation in that region. Although the refractive index of the n-typeGaAs current blocking layer 406 is greater than that of the p-typeAl_(0.5)Ga_(0.5)As cladding layer 405, the bandgap value of the n-typeGaAs current blocking layer 406 is less than that of theAl_(0.15)Ga_(0.85)As active layer 404, whereby the n-type GaAs currentblocking layer 406 absorbs light. Therefore, the generated laser lightis stably confined in a region in the vicinity of the striped portion ofthe p-type AlGaAs cladding layer 405 due to the light absorption by then-type GaAs current blocking layer 406. By setting the stripe width toabout 4 μm to about 5 μm, it is possible to obtain a single transversemode and to obtain a semiconductor laser device with excellentreliability and stability.

Next, a method for producing the semiconductor laser device of thepresent example will be described with reference to the cross-sectionalviews of FIGS. 16A to 16D.

First, as illustrated in FIG. 16A, the n-type buffer layer 402(thickness: about 0.5 μm), the n-type Al_(0.5)Ga_(0.5)As cladding layer403 (thickness: about 1.0 μm), the undoped Al_(0.15)Ga_(0.85)As activelayer 404 (thickness: about 0.08 μm), the p-type Al_(0.5)Ga_(0.5)Ascladding layer 405 (thickness: about 1.0 μm) and the intermediate layer407 (thickness: about 0.025 μm) formed of p-type Al_(0.06)Ga_(0.94)As orp-type GaAs are formed in this order on the n-type GaAs substrate 401 bythe MOCVD method.

Then, as illustrated in FIG. 16B, a mask 408 having a predeterminedpattern is formed on the layered structure produced as described aboveusing a typical photolithography technique, and a stripe-shaped ridgeportion (convex portion) is formed by an etching process. The shape ofthe mask 408 and/or the etching conditions are adjusted so that thebottom portion of the ridge portion has a width of about 4.0 μm whilethe final thickness of the p-type Al_(0.5)Ga_(0.5)As cladding layer 405is about 0.4 μm.

Thereafter, as illustrated in FIG. 16C, the n-type GaAs layer 406 isformed (regrown) on both sides of the ridge portion so as to have athickness of about 0.6 μm by an MOCVD selective growth method using themask 408.

Subsequently, after the mask 408 is removed, as illustrated in FIG. 16D,the p-type GaAs contact layer 409 is formed by the MOCVD method. Theelectrodes 410 and 411 are then formed, thereby completing thesemiconductor laser device.

During the growth process of the n-type layers 402, 403, and 406 by theMOCVD method, carbon, as well as Si as an n-type dopant, is added asdescribed above. For example, the carbon addition concentration is setto about 2×10¹⁷ cm⁻³ while the Si addition concentration is set to about2×10¹⁸ cm⁻³.

In the above production process, when the n-type GaAs current blockinglayer 406 is formed on the p-type AlGaAs cladding layer 405 by the MOCVDselective growth method as illustrated in FIG. 16C following the etchingprocess (i.e., the second MOCVD method, or the regrowth process), sincethe conductivity types are different on the opposite sides of theregrowth interface, band bending may occur. In order to prevent this, ap-type GaAs layer (not shown) having a thickness of about 0.003 μm toabout 0.05 μm, for example, may be grown between the n-type GaAs currentblocking layer 406 and the p-type AlGaAs cladding layer 405. However,the thickness of the p-type GaAs layer provided for this purpose is notlimited to the above.

Moreover, in order to reliably etch away an intended amount of thep-type Al_(0.5)Ga_(0.5)As cladding layer 405 in the etching process asillustrated in FIG. 16B, one or more Al_(k)Ga_(1−k)As layer(s) (k≧0) maybe inserted in a predetermined position within the p-typeAl_(0.5)Ga_(0.5)As cladding layer 405 so as to serve as an etching stoplayer.

EXAMPLE 5

In accordance with the present example, the n-type current blockinglayer, in the semiconductor laser device having the structureillustrated in FIG. 15, is formed of Al_(0.7)Ga_(0.3)As instead of GaAsas in Example 4. Other features regarding the structure and thematerials used as well as the employed process parameters are the sameas those of Example 4, and thus will not be further described below.

In the structure of the semiconductor laser device of the presentexample, an electric current is injected through the p-type GaAs contactlayer 409, and flows through the striped portion of the p-typeAl_(0.5)Ga_(0.5)As cladding layer 405 due to the presence of the n-typeAl_(0.7)Ga_(0.3)As current blocking layer, thereby flowing in aconcentrated manner into a region of the Al_(0.15)Ga_(0.85)As activelayer 404 beneath the striped portion and generating laser oscillationin that region. The refractive index of the n-type Al_(0.7)Ga_(0.3)Ascurrent blocking layer is less than that of the p-typeAl_(0.5)Ga_(0.5)As cladding layer 405, whereby the generated laser lightis stably confined in a region in the vicinity of the striped portion ofthe p-type AlGaAs cladding layer 405. By setting the stripe width toabout 4 μm to about 5 μm, it is possible to obtain a single transversemode and to obtain a semiconductor laser device with excellentreliability and stability.

Particularly, since the bandgap value of the n-type Al_(0.7)Ga_(0.3)Ascurrent blocking layer used in the present example is greater than thatof the Al_(0.15)Ga_(0.85)As active layer 404, the generated laser lightis not absorbed by the n-type Al_(0.7)Ga_(0.3)As current blocking layer,but is stably confined within a region in the vicinity of the stripedportion of the p-type AlGaAs cladding layer 405. Therefore, a laseroutput of about 30 mW is obtained with a cavity length of about 300 μmand a threshold current of about 35 mA, thus realizing a desirable lowcurrent operation.

As in Example 4, when the n-type Al_(0.7)Ga_(0.3)As current blockinglayer is formed on the p-type AlGaAs cladding layer 405 by the MOCVDselective growth method following the etching process (i.e., the secondMOCVD method, or the regrowth process), since the conductivity types aredifferent on the opposite sides of the regrowth interface, band bendingmay occur. In order to prevent this, a p-type Al_(0.7)Ga_(0.3)As layer(not shown) having a thickness of about 0.003 μm to about 0.05 μm, forexample, may be grown between the n-type Al_(0.7)Ga_(0.3)As currentblocking layer and the p-type AlGaAs cladding layer 405. However, thethickness of the p-type Al_(0.7)Ga_(0.3)As layer provided for thispurpose is not limited to the above.

Moreover, in order to reliably etch away an intended amount of thep-type Al_(0.5)Ga_(0.5)As cladding layer 405, one or moreAl_(k)Ga_(1−k)As layer(s) (k≧0) may be inserted in a predeterminedposition within the p-type Al_(0.5)Ga_(0.5)As cladding layer 405 so asto serve as an etching stop layer.

EXAMPLE 6

FIG. 17 is a cross-sectional view illustrating a III-V group compoundsemiconductor laser device produced in accordance with the presentexample.

In the cross-sectional view of FIG. 17, an n-type GaAs buffer layer 602,an n-type Al_(0.5)Ga_(0.5)As cladding layer 603, an undopedAl_(0.15)Ga_(0.85)As active layer 604, a p-type Al_(0.5)Ga_(0.5)Ascladding layer 605 and an n-type GaAs current blocking layer 606 areformed on an n-type GaAs substrate 601. The n-type GaAs current blockinglayer 606 is formed to have a stripe-shaped concave portion, and thep-type Al_(0.5)Ga_(0.5)As cladding layer 605 is buried to fill at leasta portion of the stripe-shaped concave portion. Thus, a current blockingstructure where the striped portion functions as a current path isformed.

A p-type GaAs intermediate layer 607 is also formed on the stripedportion, and a p-type GaAs contact layer 609 is further formed on thep-type GaAs intermediate layer 607 and the n-type GaAs current blockinglayer 606. The p-side and n-side electrodes are omitted in FIG. 17.Moreover, the formation of the p-type GaAs intermediate layer 607 may beomitted.

When producing a semiconductor laser device having the above structure,in accordance with the present example, carbon, as well as Si as ann-type dopant, is added in the growth process of an n-type layer. Thefunction of the carbon simultaneously added as described above and themethod for the simultaneous addition are similar to those described inExample 4, and will not be further described below.

In the structure illustrated in FIG. 17, an electric current is injectedthrough the p-type GaAs contact layer 609, and flows through the stripedportion of the p-type Al_(0.5)Ga_(0.5)As cladding layer 605 due to thepresence of the n-type GaAs current blocking layer 606. Thus, thecurrent flows in a concentrated manner into a region of theAl_(0.15)Ga_(0.85)As active layer 604 beneath the striped portion, andcauses laser oscillation to be generated in that region.

Although the refractive index of the n-type GaAs current blocking layer606 is greater than that of the p-type Al_(0.5)Ga_(0.5)As cladding layer605, the bandgap value of the n-type GaAs current blocking layer 606 isless than that of the Al_(0.15)Ga_(0.85)As active layer 604, whereby then-type GaAs current blocking layer 606 absorbs light. Therefore, thegenerated laser light is stably confined in a region in the vicinity ofthe striped portion of the p-type AlGaAs cladding layer 605 due to thelight absorption by the n-type GaAs current blocking layer 606. Bysetting the stripe width to about 4 μm to about 5 μm, it is possible toobtain a single transverse mode and to obtain a semiconductor laserdevice with excellent reliability and stability.

As in Example 4, when the n-type GaAs current blocking layer 606 isformed on the p-type AlGaAs cladding layer 605 by the MOCVD selectivegrowth method following the etching process (i.e., the second MOCVDmethod, or the regrowth process), since the conductivity types aredifferent on the opposite sides of the regrowth interface, band bendingmay occur. In order to prevent this, a p-type GaAs layer (not shown)having a thickness of about 0.003 μm to about 0.05 μm, for example, maybe grown between the n-type GaAs current blocking layer 606 and thep-type AlGaAs cladding layer 605. However, the thickness of the p-typeGaAs layer provided for this purpose is not limited to the above.

Moreover, in order to reliably etch away an intended amount of thep-type Al_(0.5)Ga_(0.5)As cladding layer 605, one or moreAl_(k)Ga_(1−k)As layer(s) (k≧0) may be inserted in a predeterminedposition within the p-type Al_(0.5)Ga_(0.5)As cladding layer 605 so asto serve as an etching stop layer.

EXAMPLE 7

In accordance with the present example, the n-type current blockinglayer in the semiconductor laser device having the structure illustratedin FIG. 17 is formed of Al_(0.7)Ga_(0.3)As instead of GaAs as in Example6. Other features regarding the structure and the materials used as wellas the employed process parameters are the same as those of Example 6,and thus will not be further described below.

In the structure of the semiconductor laser device of the presentexample, an electric current is injected through the p-type GaAs contactlayer 609, and flows through the striped portion of the p-typeAl_(0.5)Ga_(0.5)As cladding layer 605 due to the presence of the n-typeAl_(0.7)Ga_(0.3)As current blocking layer. Thus, the current flows in aconcentrated manner into a region of the Al_(0.15)Ga_(0.85)As activelayer 604 beneath the striped portion, and causes laser oscillation tobe generated in that region.

The refractive index of the n-type Al_(0.7)Ga_(0.3)As current blockinglayer is less than that of the p-type Al_(0.5)Ga_(0.5)As cladding layer605, whereby the generated laser light is stably confined in a region inthe vicinity of the striped portion of the p-type AlGaAs cladding layer605. By setting the stripe width to about 4 μm to about 5 μm, it ispossible to obtain a single transverse mode and to obtain asemiconductor laser device with excellent reliability and stability.

Particularly, since the bandgap value of the n-type Al_(0.7)Ga_(0.3)Ascurrent blocking layer is greater than that of the Al_(0.15)Ga_(0.85)Asactive layer 604, the generated laser light is not absorbed by then-type Al_(0.7)Ga_(0.3)As current blocking layer, but is stably confinedwithin a region in the vicinity of the striped portion of the p-typeAlGaAs cladding layer 605. Therefore, a laser output of about 35 mW isobtained with a cavity length of about 350 μm and a threshold current ofabout 35 mA, thus realizing a desirable low current operation.

As in Example 6, when the n-type Al_(0.7)Ga_(0.3)As current blockinglayer is formed on the p-type AlGaAs cladding layer 605 by the MOCVDselective growth method following the etching process (i.e., the secondMOCVD method, or the regrowth process), since the conductivity types aredifferent on the opposite sides of the regrowth interface, band bendingmay occur. In order to prevent this, a p-type Al_(0.7)Ga_(0.3)As layer(not shown) having a thickness of about 0.003 μm to about 0.05 μm, forexample, may be grown between the n-type Al_(0.7)Ga_(0.3)As currentblocking layer and the p-type AlGaAs cladding layer 605. However, thethickness of the p-type Al_(0.7)Ga_(0.3)As layer provided for thispurpose is not limited to the above.

Moreover, in order to reliably etch away an intended amount of thep-type Al_(0.5)Ga_(0.5)As cladding layer 605, one or moreAl_(k)Ga_(1−k)As layer(s) (k≧0) may be inserted in a predeterminedposition within the p-type Al_(0.5)Ga_(0.5)As cladding layer 605 so asto serve as an etching stop layer.

As described above, in each of the semiconductor light emitting devicesaccording to Examples 4 to 7, Si and carbon are both added in order toprevent the diffusion of, and thus stabilize the distribution of, thep-type dopant in the p-type layer in the DH junction structure which isthe principal portion of the light emitting device, and to efficientlyintroduce Si, which exhibits amphoteric conductivity, into the III-groupsite so that it reliably functions as an n-type dopant. Thus, theconventional problem associated with the dopant diffusion is eliminated,thereby improving the reliability of the DH junction structure.Moreover, the use of such a DH junction structure with high reliabilitymakes it possible to stably produce a high reliability semiconductorlight emitting device which realizes low current operation andlongitudinal multimode oscillation as well as low noise operation.

EXAMPLE 8

Hereinafter, another example of the present invention which realizes thesuppression of dopant diffusion will be explained. In particular, inaccordance with the present example, Si is used as an n-type dopant inan n-type cladding layer in an AlGaAs semiconductor light emittingdevice (semiconductor laser device) produced by the MOCVD method. Inaddition, the current blocking layer is provided in a two-layeredblocking structure including a Se-doped layer, as an n-type currentblocking layer closer to the p-n interface, with a Si-doped n-typecurrent blocking layer formed thereon.

FIG. 18 is a cross-sectional view illustrating a semiconductor laserdevice produced in accordance with the present example.

FIG. 18 illustrates a so-called “self-alignment” structure. Inparticular, a Si-doped n-type GaAs buffer layer 802 (carrierconcentration: about 1.5×10^(18 cm) ⁻³, thickness: about 0.5 μm), aSi-doped n-type Al_(0.5)Ga_(0.5)As cladding layer 803 (carrierconcentration: about 4×10¹⁷ cm⁻³, thickness: about 1.0 μm), an undopedAl_(0.14)Ga_(0.86)As active layer 804 (thickness: about 0.04 μm), aZn-doped p-type Al_(0.5)Ga_(0.5)As first cladding layer 805 (carrierconcentration: about 4×10^(17 cm) ⁻³, thickness: about 0.3 μm), aSe-doped n-type AlGaAs first current blocking layer 806 (carrierconcentration: about 2×10¹⁸ cm⁻³, thickness: about 0.03 μm) and aSi-doped n-type AlGaAs second current blocking layer 807 (carrierconcentration: about 3×10¹⁸ cm⁻³, thickness: about 0.8 μm) are formed inthis order on an n-type GaAs substrate 801 (carrier concentration: about2×10⁸ cm⁻³) by, for example, the MOCVD method. Then, a portion of then-type first and second current blocking layers 806 and 807 (they may bereferred to collectively as the “n-type current blocking layer”) isremoved, for example, in a striped-shape about 4 μm wide, therebyforming a current path (a striped portion) 820.

Then, a Zn-doped p-type Al_(0.5)Ga_(0.5)As second cladding layer 808(carrier concentration: about 1.5×10⁸ cm⁻³, thickness: about 1 μm) and aZn-doped p-type GaAs contact layer 809 (carrier concentration: about4×10¹⁸ cm⁻³, thickness: about 1 μm) are further formed by, for example,the MOCVD method, so as to cover the striped portion 820 and the n-typesecond current blocking layer 807. A p-side electrode 811 and an n-sideelectrode 810 are respectively formed on the p-type contact layer 809and on the reverse surface of the n-type GaAs substrate 801. The processto this point is performed while the device is still in a wafer state.

Thereafter, the wafer is cleaved into a plurality of bars, andlight-emitting facets corresponding to the opposite ends of each bar areboth coated with a predetermined reflective film. Then, the bar isdivided into a plurality of chips, thereby obtaining individualsemiconductor laser devices. Thus, a semiconductor laser device whichprovides an output of about 5 mW at an oscillation wavelength of about780 nm is obtained.

An apparatus having the structure described with reference to FIG. 3 maybe used in the MOCVD process.

In particular, in the apparatus illustrated in FIG. 3, trimethylgallium(TMGa) and trimethylaluminum (TMAl) are used as materials for III-groupelements (Ga and Al); arsine (AsH₃) as a V-group element (As) material;monosilane (SiH₄) and hydrogen selenide (H₂Se) as materials for Si andSe as n-type dopants; and diethylzinc (DEZn) as a material for Zn as ap-type dopant. A substrate is placed inside the reaction chamber (growthchamber) 30, the internal pressure of the reaction chamber 30 is set toabout 76 Torr, and the substrate temperature is set to about 750° C.using the RF coil 31. Then, the mass flow controllers (MFCs) and thevalves are appropriately controlled so as to set the ratio (V/III ratio)between the amount of supply of the material compound containing theIII-group material (i.e., the amount of supply of TMGa, or the totalamount of supply of TMGa and that of TMAl) and the amount of supply ofthe material compound containing the V-group element (i.e., the amountof supply of AsH₃) to a predetermined constant value (about 120). Then,the crystal growth process of the respective layers proceeds while theabove-described conditions are kept constant during the process.

In accordance with the conventional techniques, various problems occurdue to the fact that Se as an n-type dopant and either Zn or Mg as ap-type dopant are liable to mutual diffusion. For example, Zn as ap-type dopant doped into the p-type first cladding layer diffuses intothe n-type current blocking layer or even into the n-type cladding layerthrough the active layer, due to the effect of heat history, or thelike. On the other hand, Se as an n-type dopant doped into the n-typecurrent blocking layer or the n-type cladding layer diffuses into thep-type first cladding layer.

In order to solve the above problem, the present inventors first replacethe n-type dopant in the n-type cladding layer 803 with Si so as tosuppress the diffusion of the p-type dopant in the p-type cladding layer805 into the n-type cladding layer 803.

Moreover, the n-type current blocking layer is formed in a two-layeredstructure including the n-type first current blocking layer 806 and then-type second current blocking layer 807. Se is used as an n-type dopantfor the n-type first current blocking layer 806 on the p-type firstcladding layer 805, while Si as an n-type dopant for the n-type secondcurrent blocking layer 807 on the n-type first current blocking layer806. Thus, in a region of the p-type first cladding layer 805 locatedbeneath the n-type current blocking layer, Zn contained therein as ap-type dopant diffuses toward the n-type current blocking layer, thuscausing a pile-up phenomenon whereby the p-type and n-type dopants areboth concentrated on the n-type current blocking layer side of the p-ninterface. Zn (p-type dopant) further diffuses into the n-type currentblocking layer, and the diffusion continues until the amount of Se inthe n-type first current blocking layer 806 (the product of the Seconcentration and the thickness of the n-type first current blockinglayer 806) becomes equal to the amount of Zn in the p-type firstcladding layer 805 (the product of the preset Zn concentration and thethickness of the p-type first cladding layer 805).

If the amount of Zn in the p-type first cladding layer 805 is greaterthan the amount of Se in the n-type first current blocking layer 806, Sedoes not diffuse into the p-type first cladding layer 805. Moreover,even when the dopant concentration in the n-type first current blockinglayer 806 is varied, the current blocking function is ensured by thepresence of the n-type second current blocking layer 807.

Therefore, in the structure of the semiconductor laser device of thepresent example having such a feature, the carrier concentration of thep-type first cladding layer 805 is relatively high in the stripedportion and is relatively low outside the striped portion (i.e., beneaththe current blocking layer), so that the current is effectivelyconcentrated in the striped portion, thereby reducing the operatingcurrent.

The dopant concentration (dopant distribution) in the semiconductorlaser device produced as described above in accordance with the presentexample is measured and studied as follows.

First, layers up to the Si-doped n-type AlGaAs second current blockinglayer 807 are formed according to the above-described process, and thestriped portion 820 is formed so as to have a width of about 1000 μm,thereby obtaining a sample to be used for SIMS measurement of the dopantconcentration in the vicinity of the striped portion 820.

FIG. 19 illustrates the measured Zn and Si concentration profiles in thestriped portion 820. The results show that Zn diffuses into the activelayer 804 but does not diffuse into the n-type cladding layer 803.

FIG. 20 illustrates the measured Zn, Si and Se concentration profilesoutside the striped portion 820. FIG. 21 is an enlarged viewillustrating a portion of each of the measured Se and Zn concentrationprofiles illustrated in FIG. 20 in the vicinity of the first currentblocking layer 806. The results show that Zn diffuses into the firstcurrent blocking layer 806 but does not diffuse into the n-type secondcurrent blocking layer 807. Moreover, diffusion of Se or Si is notobserved. Thus, the Zn concentration in the portion of the p-type firstcladding layer 805 located outside the striped portion 820 (i.e.,beneath the current blocking layer 806) is about 4×10¹⁶ cm⁻³, beinglower than the dopant concentration in the other portion of the p-typefirst cladding layer 805 directly beneath the striped portion 820.

The operating current of the semiconductor laser device produced asdescribed above in accordance with the present example is typicallyabout 32 mA. Thus, it is confirmed that the semiconductor laser deviceof the present example is operable at an operating current lower thanthat (about 38 mA) of a conventional device where the n-type currentblocking layer is provided as a single Si-doped layer. Moreover, theincrease in the operating current after being continuously operated toproduce an output of about 5 mW for about 200 hours at about 70° C. istypically about 0.1 mA, which is superior to that (about 0.8 mA) of theconventional device where the n-type current blocking layer is providedas a single Si-doped layer.

In FIG. 18, some of the layers are not shown for simplicity. Inparticular, a group of etching stop layers having a two-layeredstructure is provided between the p-type first cladding layer 805 andthe n-type first current blocking layer 806. Moreover, the n-type secondcurrent blocking layer 807 is actually formed as a group of Si-dopedlayers including about four layers having respectively different crystalratios.

The respective Al mole fractions of the layers are not limited to thevalues described above. For example, the Al mole fraction of the activelayer may be zero whereby the active layer is a GaAs active layer.

Furthermore, the thickness of the active layer may be slightly reducedfrom that described above, so as to provide a 40 mW-output-classsemiconductor laser device instead of the above-described 5mw-output-class semiconductor laser device. In such a case, the optimalcarrier concentration is substantially the same as that described above.

EXAMPLE 9

In Example 8 above, the layers included in the semiconductor laserdevice having the structure illustrated in FIG. 18 are all formed by theMOCVD method. On the other hand, in accordance with the present example,the regrowth process is performed by the LPE method instead of the MOCVDmethod.

In particular, the layers from the Si-doped GaAs buffer layer 802 to theSi-doped AlGaAs second current blocking layer 807 are grown on then-type GaAs substrate 801 by the MOCVD method, and a predeterminedstriped portion 820 is formed by an etching process. Thereafter, aMg-doped p-type second cladding layer (carrier concentration: about1.5×10¹⁸ cm⁻³, thickness: about 1 μm) and a Mg-doped p-type GaAs contactlayer (carrier concentration: about 4×10¹⁸ cm⁻³, thickness: about 1 μm)are formed by the LPE method. The subsequent production processthereafter is similar to that of Example 8.

Operating characteristics comparable to those of Example 8 can berealized also in the semiconductor laser device obtained as describedabove in accordance with the present example. Moreover, the optimalcarrier concentration values of the n-type cladding layer 803 and thep-type first cladding layer 805 are substantially the same as those ofExample 8. Thus, only a slight difference results from whether theregrowth process is performed by the MOCVD method or by the LPE method.

EXAMPLE 10

FIG. 22 is a cross-sectional view illustrating a semiconductor laserdevice produced in accordance with the present example.

FIG. 22 illustrates a so-called “ridge type” structure. In particular, aSi-doped n-type GaAs buffer layer 952 (carrier concentration: about1×10₁₈ cm⁻³, thickness: about 0.5 μm), a Si-doped n-typeAl_(0.5)Ga_(0.5)As cladding layer 953 (carrier concentration: about4×10¹⁷ cm⁻³, thickness: about 1.0 μm), an undoped Al_(0.14)Ga_(0.86)Asactive layer 954 (thickness: about 0.04 μm), a Zn-doped p-typeAl_(0.5)Ga_(0.5)As first cladding layer 955 (carrier concentration:about 3×10¹⁷ cm⁻³, thickness: about 0.3 μm), a Zn-doped p-type GaAsetching stop layer 956 (carrier concentration: about 1×10¹⁸ cm⁻³thickness: about 0.003 μm), a Zn-doped p-type Al_(0.5)Ga_(0.5)As secondcladding layer 958 (carrier concentration: about 1.5×10¹⁸ cm⁻³,thickness: about 1 μm) and a Zn-doped p-type GaAs cap layer 959 (carrierconcentration: about 3×10¹⁸ cm⁻³, thickness: about 1 μm) are formed inthis order on an n-type GaAs substrate 951 (carrier concentration: about2×10^(18 cm) ⁻³) by, for example, the MOCVD method. Then, the p-type caplayer 959 and the p-type second cladding layer 958 are partially removedso as to leave a stripe-shaped ridge portion.

Thereafter, a Se-doped n-type AlGaAs first current blocking layer 960(carrier concentration: about 1×10¹⁸ cm⁻³, thickness: about 0.03 μm) anda Si-doped n-type AlGaAs second current blocking layer 965 (carrierconcentration: about 3×10¹⁸ cm⁻³, thickness: about 0.8 μm) are formed inthis order on both sides of the ridge, again by the MOCVD method. Atthis time, a portion of the n-type first and second current blockinglayers 960 and 965 (they may be referred to collectively as the “n-typecurrent blocking layer”) which has been deposited on the p-type caplayer 959 is removed by, for example, an etching process.

Then, a Zn-doped p-type GaAs contact layer 961 (carrier concentration:about 3×10¹⁸ cm⁻³) is further formed by, for example, the MOCVD method,so as to cover the p-type cap layer 959 and the n-type second currentblocking layer 965. A p-side electrode 964 and an n-side electrode 963are respectively formed on the p-type contact layer 961 and on thereverse surface of the n-type GaAs substrate 951. The process to thispoint is performed while the device is still in a wafer state.

Thereafter, the wafer is cleaved into a plurality of bars, andlight-emitting facets corresponding to the opposite ends of each bar areboth coated with a predetermined reflective film. Then, the bar isdivided into a plurality of chips, thereby obtaining individualsemiconductor laser devices.

The operating current of the semiconductor laser device produced asdescribed above in accordance with the present example is typicallyabout 34 mA, being comparable to that of the device with aself-alignment structure described above as Example 8. Moreover, theother operating characteristics are also comparable between the presentexample and Example 8. Thus, no significant characteristic difference isseen resulting from whether the device has the self-alignment structureor the ridge type structure.

As described above, in accordance with Examples 8 to 10 of the presentinvention, in the AlGaAs semiconductor light emitting device whose lightemitting portion is formed by the MOCVD method, the n-type currentblocking layer is provided in a two-layered structure including aSe-doped layer and a Si-doped layer. In particular, the Se-doped layeris closer to the p-type first cladding layer, thereby making it possibleto suppress the p-type to n-type inversion of the p-type first claddinglayer and to produce with a high production yield a semiconductor lightemitting device with satisfactory operating characteristics. Thus,reduction in the production cost of a semiconductor light emittingdevice and efficient use of the material resource are realized.

Various other modifications will be apparent to and can be readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

What is claimed is:
 1. A semiconductor light emitting device, comprising: a plurality of n-type III-V group compound semiconductor layers; a plurality of p-type III-V group compound semiconductor layers; and an active layer, wherein carbon atoms and Si atoms are both added to at least one of the plurality of n-type III-V group compound semiconductor layers.
 2. A light emitting device according to claim 1, wherein the n-type III-V group compound semiconductor layer, to which the carbon atoms and the Si atoms are both added, is in contact with at least one of the plurality of p-type III-V group compound semiconductor layers.
 3. A method for producing a semiconductor light emitting device, comprising the step of growing a layered structure on a surface of a substrate, the layered structure at least including a plurality of n-type III-V group compound semiconductor layers, a plurality of p-type III-V group compound semiconductor layers, and an active layer, wherein carbon atoms and Si atoms are both added when growing at least one layer of the plurality of n-type III-V group compound semiconductor layers. 